U.S. patent number 7,623,818 [Application Number 11/543,201] was granted by the patent office on 2009-11-24 for belt fixing device and image forming apparatus therewith.
This patent grant is currently assigned to Fuji Xerox Co., Ltd.. Invention is credited to Kazuyoshi Itoh, Yasutaka Naito, Hideaki Ohhara.
United States Patent |
7,623,818 |
Ohhara , et al. |
November 24, 2009 |
Belt fixing device and image forming apparatus therewith
Abstract
A belt fixing device includes an endless belt member, an
excitation coil and a deterioration detection unit. The endless
belt member includes a metal layer. The excitation coil heats the
metal layer by electromagnetic induction. The deterioration
detection unit detects deterioration of the metal layer of the belt
member through the excitation coil.
Inventors: |
Ohhara; Hideaki (Kanagawa,
JP), Naito; Yasutaka (Kanagawa, JP), Itoh;
Kazuyoshi (Kanagawa, JP) |
Assignee: |
Fuji Xerox Co., Ltd. (Tokyo,
JP)
|
Family
ID: |
38604946 |
Appl.
No.: |
11/543,201 |
Filed: |
October 5, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070242990 A1 |
Oct 18, 2007 |
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Foreign Application Priority Data
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Apr 18, 2006 [JP] |
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P2006-114478 |
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Current U.S.
Class: |
399/329 |
Current CPC
Class: |
G03G
15/2064 (20130101); G03G 15/553 (20130101); G03G
2215/2016 (20130101); G03G 2215/00151 (20130101); G03G
2215/2035 (20130101) |
Current International
Class: |
G03G
15/20 (20060101) |
Field of
Search: |
;399/24,67,328,329 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Brase; Sandra L
Attorney, Agent or Firm: Morgan, Lewis & Bockius LLP
Claims
What is claimed is:
1. A belt fixing device comprising: an endless belt member that
includes a metal layer; an excitation coil that heats the metal
layer by electromagnetic induction; a detection piece disposed in
an area of the belt member where a bending strain of the detection
piece is larger than that of the metal layer; and a deterioration
detection unit configured to detect, through the excitation coil,
change in a characteristic value of the detection piece, which has
a correlation with deterioration of the metal layer.
2. The belt fixing device according to claim 1, wherein the
detection piece is made of the same kind of metal as the metal
layer.
3. The belt fixing device according to claim 2, wherein the
detection piece is disposed outside an area through which a sheet
of paper having a maximum size passes.
4. The belt fixing device according to claim 2, wherein the
detection piece has 5 mm square to 30 mm square in area and has 3
.mu.m to 30 .mu.m in thickness.
5. The belt fixing device according to claim 1, wherein the
detection piece is disposed outside an area through which a sheet
of paper having a maximum size passes.
6. The belt fixing device according to claim 1, wherein the
detection piece has 5 mm square to 30 mm square in area and has 3
.mu.m to 30 .mu.m in thickness.
7. An image forming apparatus comprising a belt fixing device
according to claim 1.
Description
BACKGROUND
1. Technical Field
This invention relates to a fixing device for heating,
pressurizing, and fixing an unfixed toner image, used with an
electrophotographic-type image forming apparatus such as a copier,
a printer or a facsimile and in particular to a belt fixing device
of an electromagnetic (magnetic) induction heating system and an
image forming apparatus using the belt fixing device.
2. Description of the Related Art
Hitherto, in an electrophotographic-type image forming apparatus
such as a copier or a printer, for example, a photosensitive member
formed like a drum (photosensitive drum) is uniformly charged and
is exposed to light, which is controlled based on image
information, so as to form an electrostatic latent image on the
photosensitive drum. After the electrostatic latent image is formed
into a visible image (toner image) with toner and the toner image
is transferred from the photosensitive drum directly to a recording
medium or after the toner image is once primarily transferred to an
intermediate transfer body and is secondarily transferred from the
intermediate transfer body to a recording medium, a fixing device
fixes the toner image onto the recording medium.
A fixing device of a heating roller system is widely used as a
fixing device used in such an image forming apparatus.
In addition to such a heating roll system, a fixing device of an
electromagnetic induction heating system has also been known.
In the fixing device of an electromagnetic induction heating
system, a roller or a thin fixing belt with a metal layer is used
as a fixing member to be heated. When the thin fixing belt is used
as the fixing member, the fixing belt can be warmed up in an
extremely short time.
The main factor of determining the life of the fixing device of the
electromagnetic induction heating system using the fixing belt as
described above is a metal layer of a heat generation layer.
Generally, since the heat generation layer subjected to
electromagnetic induction heating is made of metal, the metal is
fatigue-broken because of repeated deformation in the nip portion.
As a result, the metal layer does not serve the function as the
heat generation layer. This point in time leads to the end of the
life of the fixing device of the electromagnetic induction heating
system using the fixing belt.
An effective life detection method has not yet been developed for
the fixing device of the electromagnetic induction heating
system.
SUMMARY
According to an aspect of the invention, a belt fixing device
includes an endless belt member, an excitation belt and a
deterioration detection unit. The endless belt member includes a
metal layer. The excitation coil heats the metal layer by
electromagnetic induction. The deterioration detection unit detects
deterioration of the metal layer of the belt member through the
excitation coil.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the invention will be described in detail
below with reference to accompanying drawings wherein:
FIG. 1 is a schematic drawing to schematically show the
configuration of an image forming apparatus according to an
exemplary embodiment of the invention;
FIG. 2 is a schematic sectional view of a fixing device according
to the exemplary embodiment of the invention;
FIG. 3 is a schematic front view of the fixing device according to
the exemplary embodiment of the invention;
FIG. 4 is an enlarged front view to show the configuration of a
fixing belt used in the fixing device according to the exemplary
embodiment of the invention;
FIG. 5 is a view to show variation with time in power factor in
accordance with a rotation position of a detection piece;
FIG. 6 is a view to show the linear relationship between (i) crack
occurrence cycle of a heat generation layer and/or protection layer
and (ii) crack occurrence cycle of the detection piece; and
FIG. 7 is a view to schematically show change in the maximum value
of the power factor accompanying occurrence of a crack.
DETAILED DESCRIPTION
Referring to the accompanying drawings, exemplary embodiments of
the invention will be described below.
To begin with, the schematic configuration of an image forming
apparatus to which a belt fixing device according to this exemplary
embodiment of the invention is applicable will be described with
reference to FIG. 1.
As schematically shown in FIG. 1, an image forming apparatus 10 to
which this exemplary embodiment is applicable includes a
photosensitive drum 1 on which a latent image based on the
electrostatic potential difference is formed on its surface by
applying light image to the photosensitive drum 1 after uniformly
charging the photosensitive drum 1. A charging device 2, an
exposure device 3, a developing device 5, a transfer roll 4 and a
cleaning device 6 are disposed on the surroundings of the
photosensitive drum 1. The charging device 2 uniformly charges the
surface of the photosensitive drum 1. The exposure device 3 applies
the image light to the photosensitive drum 1 to form the latent
image on the surface of the photosensitive drum 1. The developing
device 4 selectively transfers toner to the latent image formed on
the photosensitive drum 1 to form a toner image on the
photosensitive drum. The transfer roller 5 faces the photosensitive
drum 1 and generates a transfer bias electric field between the
transfer roller 5 and the photosensitive drum 1 while clamping a
recording material P therebetween. The cleaning device 6 removes
the remaining toner on the photosensitive drum 1 after the toner
image is transferred. The recording material P is fed from the
upstream of the facing part between the photosensitive drum 1 and
the transfer roller 5 in the transport direction. A fixing device 7
for heating, pressurizing and fixing the unfixed toner image
transferred onto the recording material P is disposed on the
downstream side of the facing part between the photosensitive drum
1 and the transfer roller 5 in the transport direction. Examples of
the photosensitive drum 1 may include a photosensitive drum
provided by forming on a surface of a metal drum a photosensitive
member layer made of organic photosensitive material, amorphous
selenium based photosensitive material or amorphous silicon based
photosensitive material. The charging device 2 may be provided by
coating a roller of metal having electric conductivity such as
stainless steel or aluminum with a high-resistance material. The
charging device 2 is brought into contact with the photosensitive
drum 1 to follow the rotation of the photosensitive drum 1. A
predetermined voltage is applied to the charging device 2. Thereby,
the charging device 2 produces continuous discharge in a minute gap
in the proximity of the contact portion between the charging roll 2
and the photosensitive drum 1 for almost uniformly charging the
surface of the photosensitive drum 1. The exposure device 3
generates a laser beam blinking based on an image signal. The
exposure device 3 scans the laser beam in the main scanning
direction of the photosensitive drum 1 by a polygon mirror, to
thereby form an electrostatic latent image on the surface of the
photosensitive drum 1. The developing device 4 stores black toner,
for example. The developing device 4 faces the photosensitive drum
1 while the developing device 4 and the photosensitive drum 1 are
close to each other. The developing device 4 transfers the toner in
response to the latent image on the photosensitive drum 1 to form a
visible image. The transfer roll 5 may be made of a conductive or
semiconductive roll-like member. A transfer bias voltage is applied
to the nip portion between the transfer roller 5 and the
photosensitive drum 1, to thereby transfer the toner image carried
on the photosensitive drum 1 to the recording material P. The
cleaning device 6 has a blade (not shown), for example, and presses
the blade against the surface of the photosensitive drum 1 to
scrape and remove the remaining toner on the photosensitive drum 1.
In place of the blade, the remaining toner may be scraped by a
roll-like member or may be swept out by a brush.
The fixing device 7 according to this exemplary embodiment of the
invention is implemented as a belt fixing device of an
electromagnetic induction heating system including a fixing belt 71
and a pressurization roll 72. The fixing belt 71 is subjected to
electromagnetic induction heating and is rotatable. The
pressurization roll 72 is in pressure-contact with the fixing belt
71 while being parallel to the axis of the fixing belt 71.
The image forming apparatus to which the invention is applicable is
not limited to the exemplary embodiment described above. For
example, the invention may also be applied to an image forming
apparatus of the rotary type in which an image forming unit are
placed on a rotation body. Alternatively, the invention may be
applied to an image forming apparatus of the tandem type in which
image forming units are placed side by side.
Next, the belt fixing device 7 according to this exemplary
embodiment of the invention will be described in detail with
reference to FIGS. 2 and 3. FIG. 2 is a schematic sectional view of
the belt fixing device according to the exemplary embodiment. FIG.
3 is a schematic front view of the belt fixing device according to
the exemplary embodiment. FIG. 4 is an enlarged front view to show
the configuration of the fixing belt according to the exemplary
embodiment.
As shown in FIGS. 2 and 3, the fixing device 7 according to the
exemplary embodiment includes the fixing belt 71, the
pressurization roll 72, a press pad 73 a pad support member 74, an
electromagnetic induction heating device 75 and guide members 76.
The fixing belt 71 has an endless peripheral surface. The
pressurization roll 72 abuts against the outer peripheral surface
of the fixing belt 71. The press pad 73 faces the pressurization
roll 72 and abuts against the inner peripheral surface of the
fixing belt 71 so as to press the fixing belt 71 against the
pressurization roll 72. The pad support member 74 supports the
press pad 73. The electromagnetic induction heating device 75 is
provided along the outer peripheral surface of the fixing belt 71
and heats the fixing belt 71. The guide members 76a and 76b abut
against the inner peripheral surfaces of both side edges of the
fixing belt 71. Also, a temperature sensor 77 faces the outer
peripheral surface of the fixing belt 71 and is disposed on the
upstream side of the pressure-contact portion between the
pressurization roll 72 and the press pad 73 in the rotation
direction of the fixing belt 71. The temperature sensor 77 measures
the surface temperature of the fixing belt 71.
As shown in FIG. 4, the fixing belt 71 includes a base layer 71a, a
conductive layer 71b, a protection layer 71c, an elastic layer 71d
and a surface release layer 71e in order from its inner peripheral
surface to its top layer. The base layer 71a is formed of a sheet
member having high heat resistance. The conductive layer 71b serves
as a heat generation layer and disposed on the base layer. The
protection layer 71c is disposed on the conductive layer 71b. The
elastic layer 71d is disposed on the protection layer 71c. The
surface release layer 71e forms the top layer. A primer layer may
be provided between adjacent layers so as to bond the adjacent
layers.
A flexible and heat-resistant material excellent in mechanical
strength, such as a fluorocarbon resin, a polyimide resin, a
polyamide resin, a polyamideimide resin, a PEEK resin, a PES resin,
a PPS resin, a PFA resin, a PTFE resin or FEP resin may be used as
the base layer 71a. The thickness of the base layer 71a is in a
range of about 10 .mu.m to about 100 .mu.m, preferably, in a range
of about 50 .mu.m to about 100 .mu.m (for example, 75 .mu.m) from
the viewpoint of providing compatibility between strength and
flexibility and shortening the startup time. In this exemplary
embodiment, a polyamide resin having 50 .mu.m in thickness is
used.
The conductive layer 71b is a heat generation layer, which
generates heat by the electromagnetic induction action of a
magnetic field produced by the electromagnetic induction heating
device 75. The conductive layer 71b may be formed of a metal layer,
such as iron, cobalt, nickel, copper, aluminum or chromium, having
a thickness in a range of about 1 .mu.m to about 30 .mu.m. A
material is selected so that the conductive layer 71b has a
peculiar resistance value to generate sufficient heat by
electromagnetic induction. In this exemplary embodiment, the
conductive layer 71b is made of copper having 10 .mu.m in
thickness.
The protection layer 71c is a layer for making adjustment so that
the heat generation layer (conductive layer) 71b is located in a
neutral plane in the thickness direction of the fixing belt 71. The
"neutral plane" is a plane in which bending strain does not occur
even if the fixing belt 71 deforms. Any material may be used as the
protection layer 71 so long as the protection layer has a
predetermined Young's modulus and thickness. Considering the
manufacturing cost and the heat capacity, it is desirable that the
protection layer should be formed of a metal layer. In this
exemplary embodiment, nickel having 5 .mu.m in thickness is used as
the protection layer 71c.
That is, in this exemplary embodiment, both of the conductive layer
(heat generation layer) 71b and the protection layer 71c are formed
of metal layers.
The elastic layer 71d may be made of silicone rubber, fluorocarbon
rubber or fluoro silicone rubber, which has good heat resistance
and good heat conductivity and has a thickness in a range of about
10 .mu.m to about 500 .mu.m, preferably in a range of about 50
.mu.m to about 500 .mu.m. In this exemplary embodiment, silicone
rubber having 300 .mu.m in thickness is used as the elastic layer
71d.
The surface release layer 71e is a layer for coming in direct
contact with an unfixed toner image transferred onto a recording
material P. Thus, the surface release layer 71e needs to be made of
a material having good releasability. Examples of the material of
the surface release layer 71e may include perfluoro-alkoxyfluoro
plastics (PFA), polytetrafluoroethylene (PTFE), silicone resin,
silicone rubber and fluorocarbon rubber. In this exemplary
embodiment, PFA having 30 .mu.m in thickness is used as the surface
release layer 71e.
Further, the fixing belt 71 of this exemplary embodiment includes a
detection piece 71S having a thin plate shape (thin film) serving
as a deterioration detection unit. The detection piece 71S is
disposed in a place where when the whole belt is bent, bending
stain of the detection piece 71S is larger than that of the metal
layer such as the heat generation layer 71b and/or the protection
layer 71c. Specifically, the detection piece 71S is disposed
outside the neutral plane of the fixing belt 71c in the thickness
direction of the fixing belt 71c (that is, on the front-face side
where the fixing belt 71c faces the pressurization roll 72) and
outside the heat generation layer 71b and/or the protection layer
71c, which are the metal layers. The detection piece 71S has an
area of about 5 mm square to about 30 mm square and has a thickness
in a range of about 3 .mu.m to about 30 .mu.m. Furthermore, the
detection piece 71S is disposed outside an area R through which a
sheet of paper having a maximum size passes (in the axial
direction). The detection piece 71S is used to detect deterioration
of the heat generation layer 71b and/or deterioration of the
protection layer 71c so as to determine the life of the fixing belt
71. Any material can be selected as the detection piece 71S
appropriately so long as the selected material has correlation with
deterioration of the metal layer (the heat generation layer 71b
and/or the protection layer 71c ) caused by bending of the fixing
belt 71. The metal material, which is the same as the heat
generation layer 71b or the protection layer 71c , may be adopted
as the detection piece 71S. The "same kind of metal" means that if
the metal layer is formed of plural metal layers (for example, a
copper heat generation layer and a nickel protection layer), the
detection piece is made of the same metal as any of the plural
metal layers.
In this exemplary embodiment, the detection piece 71S is disposed
outside the neutral plane of the fixing belt 71 in the thickness
direction thereof and outside the metal layers such as the heat
generation layer 71b and/or the protection layer 71c. However, the
detection piece 71S may be disposed in a place inside the fixing
belt 71 in the thickness direction thereof so long as bending
strain of the detection piece 71S is larger than that of the metal
layer such as the heat generation layer 71b and/or the protection
layer 71c.
Next, the pressurization roll 72 includes a metal cylindrical cored
bar 72a, an elastic layer 72b and a surface release layer 72c. The
metal cylindrical cored bar 72a serves as a core material. The
elastic layer 72b has heat resistance, is made of silicone rubber
or fluorocarbon rubber, and is disposed on the surface of the cored
bar 72a. The surface release layer 72c formed the outermost surface
of the pressurization roll 72. The pressurization roll 72 and the
press pad 73 form a fixing nip portion while the pressurization
roll 72 and the press pad 73 are clamping the fixing belt 71
therebetween.
The pressurization roll 72 is in pressure-contact with the press
pad 73 through the fixing belt 71 with a load of 20 kgf. The
pressurization roll 72 is driven circularly by a motor M. Also, the
fixing belt 71 is driven to follow the rotation of the
pressurization roll 72. When the recording material P to which an
unfixed toner image is transferred is passed through the fixing nip
portion between the fixing belt 71 and the pressurization roll 72,
the unfixed toner image is fixed onto the recording material P by
heat and pressure to form a fixed image.
The press pad 73 includes a pedestal 73a and an elastic member 73b.
The pedestal 73a is made of a metal such as SUS or iron, or is made
of a resin having a heat resistance. The elastic member 73b made of
silicone rubber is bonded to the pedestal 73a. The press pad 73
presses the fixing belt 71 against the pressurization roll 72. The
nip portion is formed between (i) the elastic member 73b and the
fixing belt 71 and (ii) the pressurization roll 72. In this
exemplary embodiment, to decrease mutual sliding frictional force
between the press pad 73 and the fixing belt 71, a lubricant such
as heat-resistant grease is applied to the nip portion between the
press pad 73 and the fixing belt 71.
Each guide member 76 is made of a heat-resistant resin. Each guide
member 76 includes a support part, an inner guide part 722 and an
edge guide part 723. The support part 721 supports the pad support
member 74 and is fixedly supported at its end in the axial
direction. The inner guide part 722 regulates the side edge of the
fixing belt 71. The edge guide part 723 is fitted into the
corresponding end of the fixing belt 71 in the axial direction of
the fixing belt 71.
The electromagnetic induction heating device 75 is placed along the
outer peripheral surface of the fixing device 71 with a gap having
about 2 mm from the outer peripheral surface of the fixing device.
The electromagnetic induction heating device 75 heats the
conductive layer of the fixing belt 71 by electromagnetic induction
to generate heat. The electromagnetic induction heating device 75
has a main part including a pedestal, an excitation coil 75b and an
excitation circuit 75c. The pedestal 75a has a curved surface along
the outer peripheral surface of the fixing belt 71. The excitation
coil 75b is supported on the pedestal 75a. The excitation circuit
75c supplies an AC current to the excitation coil 75b.
The pedestal 75a is made of a material having insulating properties
and heat resistance. Examples of the material of the pedestal 75a
may include a phenol resin, a polyimide resin, a polyamide resin, a
polyamideimide resin and a liquid crystal polymer resin.
The excitation coil 75b is formed into a turn part 75d (shape of
the excitation coil 75b viewed from the above), which is a litz
wire wound plural times (e.g. 11 times) into a closed loop shape
such as a rectangle shape, an oval shape or an ellipsoid shape and
extending over the substantially entire region in the axial
direction of the fixing belt 71. The litz wire is a bundle of
several copper wires each having a diameter .phi. of 0.5 mm and
insulated from each other by a heat-resistant insulating material
(for example, polyimide resin, polyamideimide resin, etc.,). The
excitation coil 75b is fixed with an adhesive to thereby be fixed
to the pedestal 75a while the shape of the excitation coil 75b is
maintained.
In the electromagnetic induction heating device 75, when an AC
current is supplied from the excitation circuit 75c to the
excitation coil 75b, a magnetic flux is generated and vanished
repeatedly in the surroundings of the excitation coil 75b. The
frequency of the AC current is in a range of about 10 kHz to about
50 kHz, for example. In this exemplary embodiment, the frequency of
the AC current is set to 30 kHz. When the magnetic flux crosses the
conductive layer 71b of the fixing belt 71, an eddy current occurs
in the conductive layer 71b so as to produce a magnetic field to
prevent change in the magnetic field and Joule heat occurs with
power proportional to the skin resistance of the conductive layer
71b (W=I.sup.2R) for heating the fixing belt 71 to a predetermined
temperature.
Next, a method for detecting deterioration of the fixing belt 71
using the detection piece 71S according to this exemplary
embodiment of the invention will be described.
Generally, if the thickness of the metal layer 71b of the heat
generation layer is in a range of about 1 .mu.m to about 30 .mu.m
as in this exemplary embodiment, as the thickness is larger,
induction heating occurs more easily, that is, the power factor is
larger. Therefore, when the detection piece 71S rotates with the
rotation of the fixing belt 71 and crosses the excitation coil 75b,
the power factor varies depending on whether or not the detection
piece 71S exists just below the excitation coil 75b. When the
detection piece 71S exists just below the excitation coil 75b, the
highest power factor is achieved.
Then, this exemplary embodiment uses the excitation coil 75b, which
serves as an electromagnetic induction heating unit, as a
deterioration detection unit. The exemplary embodiment monitors
change in the power factor of the detection piece 71S through the
excitation coil 75b. Thereby, it is made possible to detect
deterioration of the metal layer 71b, 71c of the fixing belt 71.
FIG. 5 shows variation with time of the power factor responsive to
the rotation position of the detection piece 71S, which serves as
the deterioration detection unit.
Let the rotational period of the fixing belt 71 be T.sub.0. As
understood from FIG. 5, when the detection piece 71S comes just
below the turn part 75d of the excitation coil 75b (in FIG. 5, when
time T is equal to t.sub.0+nT.sub.0 where n is an integer), the
power factor takes the maximum value.
The detection piece 71S is disposed outside the heat generation
layer 71b and/or the protection layer 71c and outside the neutral
plane of the fixing belt 71 in the thickness direction thereof.
Therefore, when the fixing belt 71 is deformed in the fixing nip
portion, bending strain occurring in the detection piece 71S
becomes larger than that occurring in the heat generation layer 71b
and/or the protection layer 71c. As a result, if the fixing belt 71
becomes deformed repeatedly in the fixing nip, deterioration
(crack) occurs on the detection piece 71S more early than the heat
generation layer 71b and/or the protection layer 71c. That is, as
schematically shown in FIG. 6, if the crack occurrence cycle (crack
occurrence time) of the detection piece 71S is the vertical axis
and the crack occurrence cycle (crack occurrence time) of the heat
generation layer 71b and/or the protection layer 71c is the
horizontal axis, it can be seen that both have a linear correlation
and the crack occurrence of the detection piece 71S is earlier than
the crack occurrence of the heat generation layer 71b/the
protection layer 71c.
When a crack occurs in the detection piece 71S, the maximum value
of the power factor detected through the excitation coil 75b
becomes small as compared with the case where no crack occurs in
the detection piece 71S. That is, as schematically shown in FIG. 7,
if the maximum value of the power factor is plotted with respect to
the time, it shows a given value to a certain point in time. When a
crack starts to occur in the detection piece 71S, the power factor
lowers almost linearly and becomes stable at another value. The
time at which a crack occurs in the detection piece 71S and the
time at which a crack occurs in the heat generation layer 71b
and/or the protection layer 71c have a linear correlation as
described above. Therefore, when the time at which a crack occurs
in the detection piece 71S is detected, it is made possible to
predict the life of the heat generation layer 71b and/or the
protection layer 71c, which determines the life of the fixing belt
71.
That is, according to the deterioration detection unit according to
this exemplary embodiment, change in the power factor of the
detection piece 71S is monitored through the excitation coil 75b.
Thereby, it is made possible to detect the precise life responsive
to the use state of the fixing belt 71, based on the predetermined
correlation between (i) the life of the heat generation layer 71b
and/or the protection layer 71c of the fixing belt 71 and (ii) the
life of the detection piece 71S.
Next, a specific examination result using such a deterioration
detection unit will be described.
To conduct an examination, first the nickel detection piece 71S
having 3 .mu.m in thickness is disposed via a thin primer layer on
the nickel protection layer 71c (having 5 .mu.m in thickness) of
the fixing belt 71 and outside the area R through which the sheet
of paper having the maximum size passes in the axial direction. The
position of the neutral plane is the center of the copper heat
generation layer 71b having 10 .mu.m in thickness by adjusting the
Young's modulus of each layer. The distance between the neutral
plane and the nickel surface of the protection layer 71c is 10
.mu.m. The distance between the neutral plane and the surface of
the detection piece 71S is 13 .mu.m.
Therefore, when the fixing belt 71 is deformed, a ratio of bending
strain occurring in the surface of the protection layer 71c to
bending strain occurring on the surface of the detection piece 71S
becomes 1:1.3 in theory.
Although the bending strain and the crack occurrence cycle do not
have a linear relation with each other in a wide range, it may be
said that 30% in difference is almost a linear relationship in
terms of the strain level in the fixing nip portion. Therefore,
letting the number of cycles until a crack starts occurring in the
detection piece 71S in the long-hour fixing operation, namely, the
number of cycles until the maximum value of the power factor starts
decreasing be Ch, it can be predicted that a crack will occur on
the protection layer 71c, namely, the end of the life will be
reached in 0.3.times.Ch cycles from the time when the crack occurs
in the detection piece 75S.
Therefore, a message indicating that the fixing belt 71 is just
before it will reach the end of the life may be displayed at an
appropriate point in time after the number of crack occurrence
cycles Ch.
Actually, occurrence of a crack in the protection layer 71c of the
fixing belt 71 in the vicinity of 1.3.times.Ch cycles under a
predetermined fixing condition can be verified. Accordingly, it can
be verified that the deterioration detection unit according to this
exemplary embodiment of the invention can detect the precise life
of the fixing belt 71 responsive to the use state of the fixing
belt 71.
In the exemplary embodiment described above, the deterioration
detection unit detects the life of the fixing belt 71 by detecting
change in the power factor of the detection piece 71S. However, the
invention is not limited to such a deterioration detection unit. A
deterioration detection unit according to another exemplary
embodiment may monitor change in the magnetic characteristic value
of the detection piece 71S having a correlation with the life of
the metal layer 71b, 71c of the fixing belt 71 through the
excitation coil 75b. For example, change in the inductance of the
detection piece 71S may be monitored through the excitation coil
75b, to thereby detect deterioration of the fixing belt 71.
Further, in the above described exemplary embodiment, the detection
piece 71S made of the same kind of metal as the metal layer 71b,
71c is disposed in the fixing belt 71 so as to detect deterioration
of the metal layer 71b, 71c from the viewpoint of stably detecting
deterioration of the metal layer with higher accuracy. However,
from the viewpoint of detecting deterioration of the metal layer
71b, 71c with a simpler configuration using a device configuration
of a related art, the detection piece 71S may be omitted and the
voltage/current of the excitation coil 75b may be monitored.
According to this configuration, deterioration of the metal layer
71b, 71c of the fixing belt 71 can also be determined. That is, in
so doing, when an actual crack occurs in the metal layer 71b, 71c,
for example, the inductance of the crack occurrence part changes
and the voltage/current induced to the excitation coil 75b changes.
Thus, although it is inferior to use of the detection piece 71S in
detection of deterioration of the metal layer 71b, 71c at rapid and
stable timing with accuracy, it is made possible to determine
deterioration of the fixing belt 71 according to the same device
configuration as that in the related art by monitoring the
voltage/current inducted to the excitation coil 75b. This
configuration contributes to drastic cost reduction and device
miniaturization as compared with a configuration provided with a
special sensor.
* * * * *